Process for treating lead ores



v Nov. 15, l938. v K.-R.GOHRIE 2,186,434

PROCESS FOR TREATING LEAD ORES Filed May 15, 1937 INVENTOR. 6 O H RE ATTORNEY.

46 KURT RUDOLF Patented Nov. 15, 1933 UNITED STATES PROCESS FOR TREATING LEAD ORES Kurt Rudolf Giihre,

Frankfort-on-the-Main,

Germany, assignor to American Lurgi Corporation, New York York, N. Y., a corporation of New Application May 13, 1937, Serial No. 142,426 In Germany May 18, 1936 11 Claims.

This invention relates to the metallurgical treatment of lead ores in the ore hearth by a roasting reaction. It is known that considerable quantities of flue dust are produced during this process, and the object of the invention is to lessen the formation of such dust. It also enables the treatment to be applied, not only to lead ores in lump form, but also to such as are in a finely divided form and have been prepared, for hearth treatment, by granulation or transformation into lump condition. Hitherto, as is known, the treatment of large charges of such granulated or agglomerated material in the ore hearth has been attended with difficulties, the formation of dust being excessive and the yield of lead too small.

According to the present invention, the object in view is achieved by lowering the reaction temperature prevailing in the hearth charge. This lowered temperature is accompanied by diminished vaporization of the lead and therefore also a smaller production of dust. It has already been the practice to cool the rear wall of the ore hearth and to pass large volumes of surplus air through and over the charge, but these measures failed to prevent. overheating of the hearth charge.

According to the invention this is achieved by employing as blastair which is blown through the tuyeres of-the ore hearth into the charge, gases which contain less oxygen than air, for example only 80 or 75% of the oxygen content of air. Thus air can be employed; the oxygen content of which has'previously been partly consumed by chemica i or metallurgical reactions, for example by combustion orv roasting processes.

Alternatively the ordinary blast air may be diluted by the addition of gases of the foregoing and difierent types, such as roasting process gases, combustion gases and the like, with the result that they contain about 1 to 10% of sulphur dioxide or carbon dioxide. It is also advantageous to blow exhaust gases from" the ore hearth in association with fresh blast air through the tuyeres of the hearth into the charge. As is known, the exhaustggases from the ore hearth contain certain quantities of sulphur dioxide, and in some in stances, carbon dioxide, owing to the presence of which the oxygen content of said gases is lower than that of the air. It has also transpired that by circulating a portion of the'exhaust gases, the reaction temperature of the hearth charge can be lowered to an extent which substantially diminishes the volatilization of the lead.

For the purpose of giving those skilled in the art, a better understanding of the present in- 'vention, reference is made to the drawing, in which:-

Fig. 1 illustrates in a more or less diagrammatic manner an embodiment of the present invention.

Fig. 2 illustrates another embodiment of the present invention in a more or less diagrammatic manner,

Fig. 3 depicts in a diagrammatic manner a third embodiment of the present invention.

A lead hearth I with the gas discharge hood 2, the water cooled back wall 3 in which nozzles 4 and the wind box 5 (tuyeres box) are arranged is shown diagrammatically in Fig. 1. The hearth is filled with lead 6 on which the charge 1 floats. The furnace gases are drawn off from the hood 2 through the fans 8 and 9. The gas stream in its entirety or a portion thereof which is drawn oif through the pipe l0 by the fan 9, the so-called returned gas, is returned to the wind box of the lead furnace through pipe Ila. On the exhaust connection of fan 9, a pipe II can be connected through which other S02 containing gases can be drawn off. The fan 8 forces the gas stream which does not recirculate to a plant for utilizing the S02 content of the gases after they have passed through a device l2 for removing the flying dust which is located in advance of the fan 8. The device l2 can be a flying dust chamber, a cyclone separator or an electric dust precipitator or the like. The fan l3 supplies fresh air to the tuyere box through the pipe 14.

In Fig. 2 a furnace with auxiliaries quite similar to that in Fig. 1 is shown. Thus, lead hearth 2| with a gas discharge hood 22 and a water cooled back wall 23 are shown. Suitably "arranged in back wall 23 are nozzles 24 and wind box 25. The hearth contains lead 26 on which a charge 21 floats. The furnace gases are drawn off from the hood 22 by suitable fans such as 28,, 29 and 33 through pipe 30 and a device 32. The gases passing through pipe 30 enter the cyclone separator 35 wherein dust particles and the like are removed. After passing through the separator 35 the purified gas stream may be divided and a portion returned to the wind box 25 by fan 29 through conduit 3|. By proper setting of the valves'3'l fan 29 may be eliminated and the cyclone separator connected directly with fan 33-which otherwise functions to supply fresh airto thetuyeres but which, with the elimination of fan 29, also functions to supply gases containing S02 to the tuyeres through conduit 34.

Likewise in Fig. 3 a furnace with auxiliaries similar to those shown in Figs. 1 and 2 is provided wherein M is a lead hearth, 42 a gasdiswhich nozzles 44 and wind box 45 are arranged. The hearth contains lead 46 on which a charge 41 floats. The furnace gases are sucked off from the hood 42 through pipe 50 into the cyclone separator 55 where it is freed from the greater portion of dust. The division of the gas stream takes place behind the cyclone separator 55. A part of the gases is conducted through the pipes 5|, 52 and 53 by the fan 48 to the tuyere box of the lead furnace while the rest of the gases are conducted by pipe 56 into a further gas purifier 58 in which it is completely freed of dust and then conducted through the pipe 59 to a plant for utilizing its S02 content The fan 49 supplies fresh air to the tuyere box through pipe 54 while the pipe 68 can service for introducing of other SO: containing gases into the tuyere box which then can replace in part of completely the returned furnace gases.

The process according to the invention is devised so that, for example, a lead ore in lump form is treated in the ore hearth. According to the invention, a portion of the exhaust hearth gases is returned to the wind box directly after issuing from the hearth, and is blown, in association with a certain amount of fresh air, through the tuyeres into the charge in the ore hearth. Owing to the sulphur dioxide and'carbon dioxide present in this flowing medium, the temperatures in the charge do not increase to anything like the same extent as when fresh air is employed for the blast.

It has now unexpectedly transpired that even,

less solid granulated or agglomerated lead ores can still be employed with advantage for this method of treatment. The quantities of flue dust contained in the partial current of exhaust gases withdrawn from circulation, remain in such cases. within the usual limits, so that they can be directly added'to the fresh ore and worked up therewith.

At the same time, there is no need to extract the dust from that portion of the hearth gases whichis returned to the wind box, inasmuch as a large portion of the dust contained in said gases is retained by the charge during the passage of the gases through the latter. All that is necessary, therefore, is careful extraction of the dust from the partial current that leaves the circulation. The sulphur dioxide concentration in the said partial current is so high as to enable the sulphur dioxide to be economically utilized. Of course, there is nothing to prevent extraction of the dust also from that portion of the hearth gases which is returned to the tuyeres, or also partial extraction of dust from the whole of the hearth gases, for example by means of flue dust chambers or cyclones and then distributing the gases so that one portion is returned direct to the tuyeres. whilst the other can be further purified before the utilization of its content of sulphur dioxide.

Of course, the process of the present invention can also be applied to the treatment of ores in the condition of lumps, or mixtures of fine ores (converted into lump form) and ores naturally in lump form, with or without addition of flue dust. The advantage of the lower reaction temperature and the attendant reduction in dust formation, is also obtained in these cases. The

extraction of dust from the exhaust gases is' facilitated, since only a portion of the hearth gases has to be cleaned, more or less completely.

In these cases, too, the sulphur dioxide in the exhaust gases can be utilized. The same result can also be obtained by supplying the ore hearth -charge hood and 43 a water cooled back wall in with other gases of similar composition to the exhaust gases from the ore hearth, such as poor roasting-furnace gases, or the exhaust gases from blast grates, upon which ores containing sulphur are sintered.

The gases may also be cooled, in known manner, prior to being returned to the tuyeres.

In my copending application Serial No. 142,425, a. process is described whereby fine lead ores are converted into lump form to prepare them for metallurgical treatment upon the ore hearth by the roasting reaction, by granulating said fine ores and thereupon heating them in such a manner as to prevent any substantial combustion of the sulphur contained in the ore. Thus for example, the heating is eifected by passing hot gases through the previously granulated material which is disposed, for example, on a grate or in a shaft. Heating is carried out up to temperatures of about 200 C. and over. More particularly at higher temperatures for example, above 400 C. gases with a lower oxygen content than air are employed as heating medium, and especially the exhaust gases from the ore hearth. After these gases have been used for heating, they can be returned wholly or partly to the ore hearth. The present invention is distinguished from this proposal by the fact that it does not relate to the granulation of fine lead ores.

I claim:-

1. The process for treating lead ores by the roasting reaction process which comprises establishing a charge containing lead ore on a furnace hearth, and forcing gases therethrough capable of supporting roasting and containing less free oxygen than air whereby molten lead is produced with less vaporization of lead.

2. The process for treating lead ores by the roasting reaction process which comprises establishing a charge containing lead ore on a furnace hearth, and blowing therethrough sulphur dioxide containing gases capable of supporting roasting and containing less free oxygen than air whereby molten lead is producedwith less vaporization of lead.

3. The process for treating lead ores by the gases being capable of supporting roasting and containing less uncombined oxygen than air whereby molten lead is produced with less va porization of lead.

4. The process for treating lead ores by the roasting reaction process which comprises establishing a charge containing lead ore on a furnace hearth, and forcing therethrough gases from a sintering operation, said gases being capable of supporting roasting and containing less free oxygen than air whereby molten lead is produced with less vaporization of lead.

5. The process for treating lead ores by the roasting reaction process which comprises establishing a charge containing lead ore on a furnace hearth, recovering gases given off by the charge, mixing a portion of said gases with air,

whilst diverting a portion of said recovered gases from the process.

6. The process for treating lead ores by the roasting reaction process which comprises establishing a charge containing lead ore on a furnace hearth, recovering gases containing sulphur dioxide given off by the charge, mixing a portion of said gases with air, forcing said mixture of recovered gases and air through said charge to produce molten lead, and utilizing the sulphur dioxide content of a portion of said recovered gases.

7. The process for treating lead ores by the roasting reaction process which comprises establishing 'a charge containing lead ore on a furnace hearth, recovering dust-laden gases given off by the charge, mixing a portion of said gases with air, forcing said mixture of recovered gases and air through said charge to produce molten lead, and separating said dust from a portion of said recovered gases.

8. The process for treating lead ores by the roasting reaction process which comprises establishing a charge containing lead ore On a furnace hearth, recovering dust-laden gases given off by said charge, freeing said gases from at least a portion of said dust, and blowing a portion of said gases at least partly freed from dust in conjunction with air through said charge to produce molten lead.

9. The process for treating lead ores by the roasting reaction process which comprises establishing a charge containing lead ore ona furnace hearth, recovering dust-laden gases given oif by said charge, freeing said gases from at least a portion of said dust, and blowing a portion of said partly dust freed gases in conjunction with air through said charge to produce molten lead while subjecting a portion of said' dust-laden gases to further dust separation.

10. In the roast reaction process for reducing lead ores to molten lead, the improvement which comprises passing gases capable ,of supporting roasting and containing less uncombined oxygen than air through an ore charge on the hearth whereby molten lead is produced.

11. In the roast reaction process for reducing lead ores to molten lead, the improvement which comprises passing gases capable of supporting roasting and containing less oxygen than air through an ore charge on a hearth whereby the reaction temperature is reduced and less lead is vaporized in the production of molten lead.

KURT RUDOLF GOHRE. 

